The invention falls within the general field of adaptations made to public facilities so that they may be used, or more conveniently used, by the handicapped, and more particularly those restricted to a wheelchair. Following the direction of this general trend, and at the prodding of federal government regulations, new buses must be provided with, and existing busses must be retrofitted with, some means of permitting use of the busses by wheelchair victims.
Over the years, different lift mechanisms have been developed to raise and lower wheelchairs, but many of these require the dedication of space, which could otherwise be used for seated passengers, to the lift mechanism. To the already financially strapped transit companies in urban areas, this type of lift is not popular. Especially during peak load times, transit operators do not want to lose additional revenue from diminished seating capacity because of spatially inefficient lifts in addition to seating capacity already lost by the inevitable occupation of more floor space by a wheelchair than by a normal passenger seat.
For this reason, transit operators and others have turned to lift mechanisms which, by virtue of converting existing stairwells alternately between stairs and lift platforms, require no additional space for their implementation. The present application, in fact, is a continuation-in-part of Patent Cooperation Treaty Application No. 80/00112, filed Feb. 23, 1980, with the United States being a designated country. The PCT application was, in fact, a continuation-in-part of U.S. Pat. No. 4,251,179 issued Feb. 17, 1981. Predecessors of that patent include U.S. Pat. No. 4,176,999 issued Dec. 4, 1979, U.S. Pat. No. 4,081,091 issued Mar. 28, 1978, and U.S. Pat. No. 4,027,807 issued June 7, 1977. This series of applications sets forth wheelchair lift technology which increases incrementally in simplification, practicality and safety, and to which line of development the present application represents the latest steps.
The basic mechanical functions of the predecessor wheelchair lift as disclosed in the parent application of this case have been carried forward to the instant device. The general technique of expanding the step panels into a flat platform by the use of hydraulics is retained, but by utilizing a novel crossed-cylinder hydraulic deployment system with a simplified slide structure, coupled with other complementary modifications, the weight of the prior device has been cut by 30 % and the number of parts slashed by 60 % to produce a unit which is significantly simpler, less subject to maintenance requirements, and is also safer and stabler in operation.